The present invention relates to the cooling of molten metal in a mold with a body or bath of molten metal which is at a lower temperature than the molten metal in the mold.
It has previously been suggested that a casting apparatus may employ a body of molten metal as a bath to promote directional solidification of an article in a mold. One apparatus for doing this is disclosed in U.S. Pat. No. 6,308,767.
During use of this known apparatus, as a portion of the mold enters the body or bath of molten metal, solidification of the molten metal in the mold is initiated by a relatively high rate of heat transfer from the mold to the upper portion of the body of molten metal. As the mold continues to move downward in the body or bath of molten metal, heat continues to be removed from the metal in the mold at a relatively high rate. This high rate of heat removal can result in excessive stressing of metal in the mold due to differential thermal contraction. These stresses can result in cracking of an article cast in the mold.